Be it known that I, B. Ryland Wiggs, 425 Sims Lane, Franklin, Tenn. 37069, have invented a new and useful xe2x80x9cThermally Exposed, Centrally Insulated Geothermal Heat Exchange Unitxe2x80x9d.
A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark office patent file or records, but otherwise reserves all copyright rights whatsoever.
The present invention relates to an improved in-ground/in-water heat exchange means for use in use in association with any heating/cooling system and/or any geothermal thermal energy generation system utilizing in-ground and/or in-water heat exchange elements as a primary or supplemental source of heat transfer.
Ground source/water source heat exchange systems typically utilize fluid-filled closed loops of tubing buried in the ground, or submerged in a body of water, so as to either absorb heat from, or to reject heat into, the naturally occurring geothermal mass and/or water surrounding the buried or submerged tubing. Water-source heating/cooling systems typically circulate water, or water with anti-freeze, in plastic underground geothermal tubing so as to transfer heat to or from the ground, with a second heat exchange step utilizing a refrigerant to transfer heat to or from the water, and with a third heat exchange step utilizing an electric fan to transfer heat to or from the refrigerant to heat or cool interior air space. Direct expansion ground source heat exchange systems typically circulate a refrigerant fluid, such as R-22, in copper underground geothermal tubing to transfer heat to or from the ground, and only require a second heat exchange step to transfer heat to or from the interior air space by means of an electric fan.
While most in-ground/in-water heat exchange designs are feasible, various improvements have been developed intended to enhance overall system operational efficiencies. Several such design improvements are taught in U.S. Pat. No. 5,623,986 to Wiggs, and in U.S. Pat. No. 5,816,314 to Wiggs, et al., the disclosures of which are incorporated herein by reference. These designs basically teach the utilization of a spiraled fluid supply line subjected to naturally surrounding geothermal temperatures, with a fully insulated fluid return line.
Other predecessor vertically oriented geothermal heat exchange designs are disclosed by U.S. Pat. No. 5,461,876 to Dressler, and by U.S. Pat. No. 4,741,388 to Kuriowa. Dressler""s xe2x80x9c876xe2x80x9d patent teaches the utilization of an in-ground spiraled fluid supply line, but neglects to insulate the fluid return line, thereby subjecting the heat gained or lost by the exiting circulating fluid to a xe2x80x9cshort-circuitingxe2x80x9d effect as the return line comes in close contact with the warmest or coldest portion of the entering fluid supply line. Kuriowa""s preceding xe2x80x9c388xe2x80x9d patent is virtually identical to Dressler""s subsequent claim, but better, because Kuriowa insulates a portion of the return line, via surrounding it with insulation, thereby helping to reduce the xe2x80x9cshort-circuitingxe2x80x9d effect. Dressler""s xe2x80x9c876xe2x80x9d patent also discloses the alternative use of a pair of concentric tubes, with one tube being within the core of the other, with the inner tube surrounded by insulation or a vacuum. While this multiple concentric tube design reduces the xe2x80x9cshort-circuitingxe2x80x9d effect, it is practically difficult to build and could be functionally cost-prohibitive.
The disadvantage encountered with insulating the heat transfer return line, by means of fully surrounding a portion of same with insulation as per Kuriowa, or by means of a fully insulated concentric tube within a tube as per Dressler, or by means of a fully insulated return line as per Wiggs"" predecessor designs, is that the fully insulated portion of the return line is not exposed to naturally occurring geothermal temperatures, and is therefore a costly necessary underground/underwater system component which is not capable of being utilized for geothermal heat transfer purposes. While the utilization of such fully insulated costly components is an improvement over prior totally un-insulated geothermal heat transfer line designs subject to a xe2x80x9cshort-circuitingxe2x80x9d of the maximum heat gain/loss potential, a design which insulates the supply line from the return line and still permits both lines to retain natural geothermal heat exchange exposure would be preferable.
It is an object of the present invention to further enhance and improve the efficiency and installation cost functionality of predecessor geothermal heat exchange designs. This is accomplished by means of insulating the underground and/or underwater heat transfer fluid supply line, or lines, from the fluid return line, or lines, while still providing for natural geothermal heat exchange exposure along the entire length of both the supply line, or lines, and the return line, or lines.
To accomplish this objective, in a vertically oriented borehole for example, insulation, which is non-corrosive to fluid supply and return line tubing, is inserted between the supply line, or lines, and the return line, or lines, across the entire central diameter of the hole, with the supply line, or lines, on one side of the centrally located insulation, and the return line, or lines, on the other side. The borehole may be an open hole drilled into the ground, or may be a hole drilled into the ground within which a heat conductive casing, such as a metal water-well casing, is placed along the exterior perimeter of the hole, directly adjacent to, and in thermal contact with, the ground. Each respective side of the centrally located insulation, containing the respective supply and return lines, would then be filled with a non-corrosive, heat conductive, fill material, such as a thermal grout 85 mixture. As a result, during system operation, the supply and the return lines will each transfer heat to or from their respective surrounding non-corrosive, heat conductive, fill material, with both the respective supply and return lines and their respective surrounding non-corrosive, heat conductive, fill material separated from each other by insulation. In turn, each respective combination of heat exchange line and its surrounding non-corrosive, heat conductive, fill material will transfer heat to or from the adjacent sub-surface ground and/or water. If the insulation width at the exterior edge of the borehole does not exceed one-third of the borehole""s diameter, each respective combination of heat exchange line and its surrounding non-corrosive, heat conductive, fill material will be exposed to about 140 degrees of earth and/or water, for geothermal heat exchange purposes, for the entire depth and/or length of the borehole, absent any material xe2x80x9cshort circuitingxe2x80x9d effect. The earth on the opposite sides of the centrally insulated borehole will be relatively unaffected by the heat transfer on the other side so long as the central insulation, separating the supply and return lines, extends for the greater distance, as measured from one side of the borehole to the other, of at least three times, and preferably four times, the diameter of the largest geothermal fluid transfer line, and at least three times, and preferably four times, the combined diameter of the largest multiple fluid transfer lines on either respective side of the central insulation. The width of separating insulation will generally be restricted by the borehole width, consequently, the borehole should be drilled at a diameter of sufficient width to accommodate at least this minimum insulation distance.
An additional advantage of surrounding the copper refrigerant supply and return lines with a non-corrosive, thermally conductive, fill material, such as a thermal grout 85 mixture, is that it eliminates the necessity for cathodic protection of the in-ground copper if the soil and/or ground water is too acidic, less than a 5.5 pH, or too basic, greater than a 12 pH. In the event corrosive soil and/or water is encountered, the centrally located separating insulation should only extend to within one-half inch to one inch of the outside perimeter of the borehole so as to permit the thermally conductive fill material to fully enclose and encapsulate the supply and the return lines as well as the central insulation, forming a complete protective exterior shell against corrosive elements which could otherwise potentially migrate to the supply and return lines. Even though some minimal heat migration between the supply and the return lines will occur as a result of the connected one-half inch to one inch thermally conductive fill material along the outside perimeter of the borehole, such a minimal xe2x80x9cshort circuitingxe2x80x9d effect will be relatively insignificant, and this minor disadvantage will be more than offset by this highly advantageous and effective means of insuring the supply and return lines will not become corroded, which could result in overall system operational failure by means of leaks in one or both of the supply and return lines. Utilization of at least a one-half inch thick non-corrosive, thermally conductive, fill material to protect the fluid transport lines against potentially corrosive sub-surface conditions, as described above, is a better and improved method over a simple thin coating of the fluid transport tubes with a non-corrosive substance. This is because one small pinhole prick in a simple thin coating will totally invalidate the intended protective integrity in a sub-surface corrosive environment.
The insulation area between the supply and return lines at the center of the borehole may be optionally expanded in area so as to reduce the amount of heat conductive fill required, and so as to increase thermal insulation quality. Other than at any such optionally expanded insulated center of the borehole, it is also important not to exceed an insulation width of more than one-third the diameter of the borehole on each respective side where the insulation contacts the ground, or where the insulation meets the borehole encasement piping which is directly adjacent to the ground, at the exterior side of the borehole. Otherwise, the advantageous expanded ground surface contact area, resulting from the heat conductive fill material surrounding the respective fluid transfer lines, will be unduly impaired. With a per side borehole insulation width equal to one-third of the borehole""s diameter, there will still be about 77.7% of the 180 degrees per respective circumference side of the borehole available for geothermal heat transfer, or about 140 respective available circumference degrees per respective side available for geothermal heat transfer.
In order to avoid adverse geothermal heat transfer affects as a result of near-surface heat conditions, such as frosting in the winter and scorching in the summer, both the supply and the return subterranean fluid transfer lines should be fully insulated from between two to ten feet below the frost and/or the heat line in any geographic location. All above-ground fluid supply lines and all above-ground fluid return lines should be fully insulated with rubatex or the like. As these near-surface insulation procedures are both customary and obvious, such near-surface insulation procedures are not shown in the drawings.
For a direct expansion system, this invention will additionally easily permit the installation of a smaller liquid line on one side of the central insulation and the installation of a larger vapor line on the other side, with both lines exposed to the sub-surface ground and/or water, thereby facilitating a reverse cycle operation in both the heating and the cooling modes where the refrigerant flow reverses direction, depending on the desired heating or cooling mode performance. For example, in the heating mode, the ground""s natural geothermal heat content operates as the evaporator, with the cold liquid refrigerant flowing into the smaller liquid line and the warmed refrigerant vapor flowing out the larger vapor line. In the cooling mode, the ground""s natural geothermal heat content operates as the condenser, with the hot refrigerant vapor flowing into the larger vapor line and the cooled liquid refrigerant flowing out the smaller liquid line.
In a deep borehole direct expansion application, beyond 50 to 100 feet deep, a well-known oil-separator should be attached to the system""s compressor unit so as to prevent loss of internal compressor lubricating oil into the low geothermal line at the bottom of the borehole. As the use of an oil-separator to prevent loss of compressor lubrication into fluid supply and return lines is well-known, this aspect is not shown in the drawings. Other customary direct expansion refrigerant system apparatus and materials would be utilized in a direct expansion system application, including a receiver, a thermal expansion valve, an accumulator, and an air-handler, for example as described in U.S. Pat. No. 5,946,928 to Wiggs, all of which are well-known to those in the trade.
The subject invention may be utilized as an individual unit, or by means of multiple units connected by tubing in series or in parallel so as to avoid excessively deep applications. As the manner of connecting multiple units in series or in parallel by means of tubing would be readily understood by those skilled in the trade, this aspect is not shown in the drawings. The subject invention may be utilized as a sub-surface heat exchange unit to increase operational efficiencies and/or to reduce installation costs in a number of applications, such as in a conventional geothermal closed-loop water-source heat pump system, in a conventional geothermal direct expansion heat pump system, as a supplement to a conventional air-source heat pump system, or the like. The invention may also be utilized to assist in efficiently heating or cooling air by means of a forced air heating/cooling system, or may be utilized to assist in efficiently heating or cooling water in a hydronic heating/cooling system.
The subject invention may be installed in a variety of optional manners, such as in a borehole, inside of a casing placed within a borehole, inside of a lateral or angled trench, inside of a casing placed within a lateral or angled trench, inside of a casing placed in water, or in any other like or similar manner. If the subject invention is placed within a casing, which casing is installed in the ground or in the water, the lower bottom end of the casing should be capped and sealed so as to assist in preventing any potentially corrosive soil and/or water from migrating to the supply and return lines within the sub-surface portion of the casing.